Previous LectureThe 7d plenoptic function, indexing all light.
Lightfields: a 4d (not 5d!) data structure which captures all outgoing light from a region and permits reconstruction of arbitrary synthetic viewpoints. Can be built into a modern camera.
Capturing and recreating visual contentinvolves a combination of geometricand image-based methods.
Lytro Camera
Image-Based Lighting
cs129: Computational PhotographyJames Hays, Brown, Fall 2012
© Eirik Holmøyvik
Slides from Alexei Efros and Paul Debevec
Inserting Synthetic Objects
Why does this look so bad?• Wrong orientation• Wrong lighting• No shadows
SolutionsWrong Camera Orientation
• Estimate correct camera orientation and render object– Requires camera calibration to do it right
Lighting & Shadows• Estimate (eyeball) all the light sources in the scene and
simulate it in your virtual rendering
But what happens if lighting is complex? • Extended light sources, mutual illumination, etc.
Environment Maps
Simple solution for shiny objects• Models complex lighting as a panoramic image• i.e. amount of radiance coming in from each direction• A plenoptic function!!!
reflective surface
viewer
environment texture image
v
n
r
projector function converts reflection vector to texture image (u, v)
Environment Mapping
Reflected ray: r=2(n·v)n-v
Texture is transferred in the direction of the reflected ray from the environment map onto the objectWhat is in the map?
What approximations are made?The map should contain a view of the world with the
point of interest on the object as the Center of Projection• We can’t store a separate map for each point, so one map is
used with the COP at the center of the object• Introduces distortions in the reflection, but we usually don’t
notice• Distortions are minimized for a small object in a large room
The object will not reflect itself!
Environment MapsThe environment map may take various forms:
• Cubic mapping• Spherical mapping• other
Describes the shape of the surface on which the map “resides”
Determines how the map is generated and how it is indexed
Cubic Mapping
The map resides on the surfaces of a cube around the object• Typically, align the faces of the cube with the coordinate axes
To generate the map:• For each face of the cube, render the world from the center of
the object with the cube face as the image plane– Rendering can be arbitrarily complex (it’s off-line)
To use the map:• Index the R ray into the correct cube face• Compute texture coordinates
Cubic Map Example
Sphere MappingMap lives on a sphere
To generate the map:• Render a spherical panorama from the designed center
point
To use the map:• Use the orientation of the R ray to index directly into the
sphere
Example
What about real scenes?
From Flight of the Navigator
What about real scenes?
from Terminator 2
Real environment mapsWe can use photographs to capture environment maps
How do we deal with light sources? Sun, lights, etc?• They are much much brighter than the rest of the
enviarnment
User High Dynamic Range photography, of course!
Several ways to acquire environment maps:• Stitching mosaics• Fisheye lens• Mirrored Balls
Stitching HDR mosaicsStitching HDR mosaics
http://www.gregdowning.com/HDRI/stitched/http://www.gregdowning.com/HDRI/stitched/
Scanning Panoramic CamerasScanning Panoramic CamerasPros:
very high res (10K x 7K+)Full sphere in one scan – no stitchingGood dynamic range, some are HDR
Issues:More expensiveScans take a while
Companies: Panoscan, Sphereon
Pros:very high res (10K x 7K+)Full sphere in one scan – no stitchingGood dynamic range, some are HDR
Issues:More expensiveScans take a while
Companies: Panoscan, Sphereon
Fisheye ImagesFisheye Images
Mirrored SphereMirrored Sphere
Sources of Mirrored BallsSources of Mirrored Balls
2-inch chrome balls ~ $20 ea. e.g. McMaster-Carr Supply Company
www.mcmaster.com
6-12 inch large gazing balls
Hollow Spheres, 2in – 4in e.g. Dube Juggling Equipment
www.dube.com
FAQ on http://ict.debevec.org/~debevec/HDRShop/main-pages/tutorials.html
2-inch chrome balls ~ $20 ea. e.g. McMaster-Carr Supply Company
www.mcmaster.com
6-12 inch large gazing balls
Hollow Spheres, 2in – 4in e.g. Dube Juggling Equipment
www.dube.com
FAQ on http://ict.debevec.org/~debevec/HDRShop/main-pages/tutorials.html
0.34 0.34
0.580.58
=> 59% Reflective=> 59% Reflective
Calibrating Mirrored Sphere Reflectivity
Calibrating Mirrored Sphere Reflectivity
Real-World HDR Lighting Environments
Lighting Environments from the Light Probe Image Gallery:http://www.debevec.org/Probes/Lighting Environments from the Light Probe Image Gallery:http://www.debevec.org/Probes/
FunstonBeach
UffiziGallery
EucalyptusGrove
GraceCathedral
Acquiring the Light ProbeAcquiring the Light Probe
Assembling the Light ProbeAssembling the Light Probe
Not just shiny…Not just shiny…
We have captured a true radiance map
We can treat it as an extended (e.g spherical) light source
Can use Global Illumination to simulate light transport in the scene So, all objects (not just shiny) can be
lighted What’s the limitation?
We have captured a true radiance map
We can treat it as an extended (e.g spherical) light source
Can use Global Illumination to simulate light transport in the scene So, all objects (not just shiny) can be
lighted What’s the limitation?
Illumination ResultsIllumination Results
Comparison: Radiance map versus single imageComparison: Radiance map versus single image
Putting it all togetherPutting it all together
Synthetic Objects +Real light!
Synthetic Objects +Real light!
CG Objects Illuminated by a Traditional CG Light Source
CG Objects Illuminated by a Traditional CG Light Source
Paul Debevec. A Tutorial on Image-Based Lighting. IEEE Computer Graphics and Applications, Jan/Feb 2002.
Paul Debevec. A Tutorial on Image-Based Lighting. IEEE Computer Graphics and Applications, Jan/Feb 2002.
Rendering with Natural LightRendering with Natural Light
SIGGRAPH 98 Electronic Theater
RNL Environment mapped onto
interior of large cube
MOVIE!MOVIE!
Illuminating a Small SceneIlluminating a Small Scene
We can now illuminatesynthetic objects with real light.
How do we add synthetic objects to a real scene?
We can now illuminatesynthetic objects with real light.
How do we add synthetic objects to a real scene?
Real Scene ExampleReal Scene Example
Goal: place synthetic objects on tableGoal: place synthetic objects on table
Light Probe / Calibration GridLight Probe / Calibration Grid
real scenereal scene
Modeling the SceneModeling the Scene
light-based modellight-based model
The Light-Based Room ModelThe Light-Based Room Model
real scenereal scene
Modeling the SceneModeling the Scene
synthetic objectssynthetic objects
light-based modellight-based model
local scenelocal scene
The Lighting ComputationThe Lighting Computation
synthetic objects(known BRDF)
synthetic objects(known BRDF)
distant scene (light-based, unknown BRDF)distant scene (light-based, unknown BRDF)
local scene(estimated BRDF)
local scene(estimated BRDF)
Rendering into the SceneRendering into the Scene
Background PlateBackground Plate
Rendering into the SceneRendering into the Scene
Objects and Local Scene matched to SceneObjects and Local Scene matched to Scene
Differential RenderingDifferential Rendering
Local scene w/o objects, illuminated by modelLocal scene w/o objects, illuminated by model
Differential Rendering (2)Difference in local sceneDifferential Rendering (2)Difference in local scene
-- ==
Differential RenderingDifferential Rendering
Final ResultFinal Result
IMAGE-BASED LIGHTING IN FIAT LUXPaul Debevec, Tim Hawkins, Westley Sarokin, H. P. Duiker, Christine Cheng, Tal Garfinkel, Jenny Huang
SIGGRAPH 99 Electronic Theater
HDR Image SeriesHDR Image Series
2 sec2 sec 1/4 sec1/4 sec 1/30 sec1/30 sec
1/250 sec1/250 sec 1/2000 sec1/2000 sec 1/8000 sec1/8000 sec
Stp1 PanoramaStp1 Panorama
Assembled PanoramaAssembled Panorama
Light Probe ImagesLight Probe Images
Capturing a Spatially-Varying Lighting EnvironmentCapturing a Spatially-Varying Lighting Environment
The MovieThe Movie
Simulating the Glare in the Human Eye
Simulating the Glare in the Human Eye
• Greg Spencer, Peter Shirley, Kurt Zimmerman, and Donald Greenberg. Physically-based glare effects for digital images. SIGGRAPH 95.
• Greg Spencer, Peter Shirley, Kurt Zimmerman, and Donald Greenberg. Physically-based glare effects for digital images. SIGGRAPH 95.
Scattering in the eye
What’s the scattering model?
HDR Image
Gaussian Blur, LDR information Only
Gaussian Blur, Full HDR Information
Full HDR Disc Blur
Frame Postprocessing in Rendering with Natural Light
Frame Postprocessing in Rendering with Natural Light